U079D - Understanding Common in 2016-2020 Chevrolet Silverado and GMC Sierra

Quick Answer

U079D means: U079D indicates a communication failure between the Body Control Module and Transmission Control Module.

Fix: Check and replace faulty components Cost: $400 - $800 Time: 90-180 minutes

Can I drive with U079D? Immediate attention is recommended to prevent further damage to the transmission system.

Common Questions

What does U079D mean and how does it affect my car?

The U079D code indicates a communication failure between the Body Control Module and the Transmission Control Module. This can lead to issues like erratic shifting or loss of electrical functions, significantly affecting your vehicle's performance and safety.

What are the most common causes of U079D and how much does it cost to fix?

Common causes include a faulty BCM, damaged wiring, or software issues, with repair costs ranging from $50 for software updates to $800 for BCM replacement.

Can I drive my car with U079D or should I stop immediately?

It's advisable to stop driving the vehicle and have it diagnosed. Continuing to drive could lead to more significant transmission problems and safety risks.

How can I diagnose U079D myself using GeekOBD APP?

Using the GeekOBD APP, perform an OBD2 scan to check for DTCs, review freeze frame data for context, and look for any additional codes that may help in diagnosing the issue.

What vehicles are most commonly affected by U079D?

Vehicles commonly affected include the 2016-2020 Chevrolet Silverado and GMC Sierra, among others. Be sure to check for any recalls or Technical Service Bulletins (TSBs) related to this issue.

How can I prevent U079D from happening again?

Regular maintenance, including inspecting wiring and connectors for wear, keeping software updated, and addressing any electrical issues promptly, can help prevent the recurrence of U079D.

What is U079D?

The diagnostic trouble code (DTC) U079D indicates a communication issue between the vehicle's control modules, specifically related to the Body Control Module (BCM) and the Transmission Control Module (TCM). In simpler terms, this means that the BCM is having trouble sending or receiving information from the TCM. This can lead to various performance issues in your vehicle, including erratic shifting in automatic transmissions or even complete transmission failure in severe cases. When this code appears, it's essential to understand that it can affect the overall functionality of the vehicle. Symptoms might include the check engine light being illuminated, transmission not engaging properly, or even loss of power steering in some cases. Ignoring this code could lead to more severe issues down the line, potentially causing costly repairs. For owners of vehicles like the 2016-2020 Chevrolet Silverado or GMC Sierra, it's crucial to address this issue promptly. Regular diagnostics and maintenance can help prevent further complications, ensuring your vehicle operates smoothly and efficiently. If you encounter this code, consider using a diagnostic tool like the GeekOBD APP to retrieve additional codes and freeze frame data, providing deeper insights into the problem.

System: U - Network (Communication, CAN Bus)

Symptoms

Common symptoms when U079D is present:

  • Check engine light stays on constantly, indicating a persistent issue that needs addressing.
  • Transmission may hesitate or struggle to shift, causing a jerking motion during acceleration.
  • Loss of certain electrical functions, such as power windows or locks, may occur intermittently.
  • In some cases, the vehicle may enter 'limp mode', restricting speed and functionality to prevent further damage.
  • Fuel economy may noticeably decrease as the transmission struggles to operate efficiently.

Possible Causes

Most common causes of U079D (ordered by frequency):

  1. The most common cause of U079D is a faulty body control module, with an estimated likelihood of around 60%. This can occur due to water damage, electrical shorts, or manufacturing defects.
  2. Another significant cause is damaged wiring or connectors between the BCM and TCM, which can be attributed to wear and tear or poor maintenance. This issue accounts for about 25% of cases.
  3. A third potential cause could be software issues within the control modules, requiring a simple reprogramming or update to resolve the problem. It's essential to stay current with software updates.
  4. Less commonly, a malfunctioning transmission control module may trigger this code. This could lead to serious transmission performance issues if not addressed.
  5. In rare instances, the issue may stem from a more complex electrical fault within the vehicle's communication network, often requiring advanced diagnostics to identify.

U079D Repair Costs

Cost Breakdown by Repair Type

Body Control Module Replacement

Replacing a faulty BCM with a new or refurbished unit. This often involves reprogramming the new module to ensure compatibility.

  • Total: $400 - $800
  • Success rate: 85%
Wiring Repair

Repairing or replacing damaged wiring and connectors between the BCM and TCM.

  • Total: $100 - $300
  • Success rate: 90%
Software Update

Updating the software in the BCM or TCM to fix communication issues.

  • Total: $50 - $150
  • Success rate: 75%
Money-Saving Tips for U079D
  • Start with the most common and least expensive repairs first
  • Use GeekOBD APP to confirm diagnosis before replacing expensive parts
  • Consider preventive maintenance to avoid future occurrences
  • Compare prices for OEM vs aftermarket parts based on your needs
  • Address the issue promptly to prevent more expensive secondary damage

Diagnostic Steps

Professional U079D Diagnosis Process

Follow these systematic steps to accurately diagnose U079D. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion (5-10 minutes)

Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion (5-10 minutes). Look particularly around the BCM and TCM.

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 2: Step 2: Use the GeekOBD APP to perform an OBD2 scan - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes)

Step 2: Use the GeekOBD APP to perform an OBD2 scan - Retrieve all codes and freeze frame data to understand the fault context (10-15 minutes). This provides a clearer picture of the issue.

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 3: Step 3: Conduct component testing - Use a multimeter or specific diagnostic tools to test the BCM and TCM for functionality (20-30 minutes)

Step 3: Conduct component testing - Use a multimeter or specific diagnostic tools to test the BCM and TCM for functionality (20-30 minutes). Verify voltage levels and continuity.

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 4: Step 4: System function test - After repairs, verify proper operation of all related systems and clear codes to ensure the issue has been resolved (10-15 minutes)

Step 4: System function test - After repairs, verify proper operation of all related systems and clear codes to ensure the issue has been resolved (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and ensure all systems are functioning normally (15-20 minutes)

Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and ensure all systems are functioning normally (15-20 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.

Important Notes

  • Always verify the repair with GeekOBD APP after completing diagnostic steps
  • Clear codes and test drive to ensure the problem is resolved
  • Address underlying causes to prevent code recurrence

Real Repair Case Studies

Case Study 1: 2018 Chevrolet Silverado - Erratic Shifting Issue

Vehicle: 2018 Chevrolet Silverado 1500, 45,000 miles

Problem: Customer reported that the vehicle's transmission hesitates and shifts erratically.

Diagnosis: After using the GeekOBD APP, the U079D code was retrieved, indicating a communication failure between the BCM and TCM. Further inspection revealed damaged wiring.

Solution: Replaced the damaged wiring harness and reprogrammed the BCM. All systems restored to normal.

Cost: $500 (including parts and labor)

Result: The vehicle's performance improved significantly, with no further issues reported after the repair.

Case Study 2: 2019 GMC Sierra - Check Engine Light On

Vehicle: 2019 GMC Sierra 1500, 30,000 miles

Problem: Customer noticed the check engine light was illuminated constantly.

Diagnosis: An OBD2 scan revealed the U079D code, which led to further testing of the BCM and TCM. A software update was necessary.

Solution: Performed a software update on the BCM, which resolved the communication issues.

Cost: $100 (for the software update)

Result: The check engine light was cleared, and the vehicle operated normally, with no further issues reported.

Diagnose U079D

Use GeekOBD APP for professional diagnosis!

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  • Professional-grade analysis
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Code Information

Code: U079D
System: Network (Communication, CAN Bus)
Severity: HIGH
Category: Network Codes